Geological Society. 327 
to certain groups of strata, and it is remarkable that so vast an 
accession of new species offers but few exceptions to the rule. 
In the chalk two species have come to light belonging to genera 
before observed in the oolitic series only, and a distinct species of 
one of these genera extends even into the lower or Eocene tertiary 
deposits. 
The labours of Mr. Charlesworth have thrown much light on the 
structure of the crag of Suffolk and Essex, and on the fossils of 
that deposit. He proposes to divide the crag into the upper or red 
crag, and the lower or coralline crag, the last of which consists for 
the most part of calcareous sand, derived chiefly from the decom- 
position of zoophytes and shells, and in which many very perfect 
corals and testacea are preserved. Among other places this coral- 
line crag may be well examined at Tattingstone, Ramsholt, Orford, 
and Aldborough. It is now many years since Mr. Wood, of Hes- 
kerton in Suffolk, formed a large collection of crag fossils, amount- 
ing in number to no less than 450 species of the classes Annulata, 
Cirrhipeda, Conchifera, and Mollusca. Out of 370 species of shells 
found in the lower crag, Mr. Wood identifies 150 with those found 
in the red crag. Of these 150 species, common to the two deposits, 
Mr. Charlesworth suggests that many may have belonged to the 
lower bed and have been washed into the newer one, in the same 
manner as some fossil shells of the chalk have been evidently im- 
bedded in the crag*. 
Such accidental mixtures have doubtless occurred, and they have 
been occasionally remarked by geologists in other places under 
analogous circumstances. But I continue to believe that these 
upper and lower divisions of the crag should be referred to the 
same geological period. The determination of that period or the 
exact place which the crag should occupy in the chronological series 
of European strata is a more difficult question. When I first sub- 
mitted 111 species of crag shells to the examination of M. Deshayes, 
he was of opinion that 66 of them were extinct, and that the others 
belonged to recent species now inhabitants of the Germian Ocean. 
I lately laid before him 60 species from the coralline crag with which 
Mr. Charlesworth had favoured me, and he was still of opinion that 
the proportion of recent species was equally great. 
But I should add that the suites of individuals of each species 
were not so full and complete as might have been desired, to enable 
these identifications to be placed beyond all doubt. Dr. Beck 
has lately seen 260 species of crag shells in Mr. Charlesworth’s ca- 
binet in London, and informs me, that although a large proportion of 
the species approach very near to others which now live in our nor- 
thern seas, he regards them as almost all of distinct species,.and un- 
known as living. Both he and M. Deshayes have declared the 
shells to be those of a northern climate, and according to Dr. Beck 
the climate may even have resembled that of our arctic regions. 
* [See Mr. Charlesworth’s paper on the Crag, in L. and E. Phil, Mag. 
vol. vii. p. 81; also p, 413, note, and p, 464 of the same volume. ] 
